[misterno]

My 12 year old Ruud gas furnace was equipped with a Fasco inducer motor that went bad when the squirrel wheel lost teeth. I replaced it with a Fasco A136 which is the called for replacement. I also replaced the vent pressure switch with an OEM replacement unit. The motor runs but according to a service tech it does not put out enough vacuum to close the switch. ( at that point I exchanged the A136 for another from the dealer) Manual suction will operate the switch and the furnace will start. Also the furnace will start and run if I use a jumper to by-pass the switch. I tried a small amount of sealant, motor to furnace but it made no difference. I also tried using various lengths of tubing (motor to switch). Any ideas on how to increase the vacuum (from .9+ to 1.11 required) or any thoughts on what I have overlooked would be most appreciated. Thanks, Bill

 

[yuri]

I would get a OEM one from Rheem as sometimes the aftermarket ones don't have the same rpms. Usually Fasco is OK but I have not seen the exact one you have.

Check your chimney for blockage if it is a mid efficiency furnace. If high efficiency check the vent pipes.

Use a drill bit or nail and where the pressure switch tube attaches to the furnace poke it thru in case there is a blockage.

Rheem had a different rated pressure switch to go with some of the replacement inducers as there were switch tripping problems. Cannot remember the rating.

Point being sometimes it is best to use OEM Rheem parts. When installing the inducer it should come with a new gasket. If not use red or black high temp RTV silicone.

 

[misterno]

Thanks Yuri, I will contact Ruud/Rheem about a lower rated pressure switch. The original inducer motor on my Ruud was a Fasco and the replacement I bought was right from their spec/replacement book. If I could figure out how to get the squirrel wheel off the original motor maybe I could swap it for the one on the replacement and reinstall the original motor. Thanks too for the tip on the sealant.
Have a great New Year!
Bill

 

[yuri]

They may not "Have" a lower rated switch but some Brands later on have TSB's technical service bulletins which may have a different switch if they had venting problems or changes to the inducer. One of their 80% mid efficient units did.

Do you have a high efficiency unit with plastic venting or a mid eff with a chimney?

 

[beenthere]

Could also be that the heat exchanger is cracked.

 

[roughneck]

You cannot just put a lower rated pressure switch on the unit because the OEM one doesn't work, without the manufacturers approval.
You either have the incorrect inducer, a faulty inducer, a blocked vent or a heat exchanger issue.

 

[misterno]

Thanks to all. My furnace is a 90% with plastic vent pipe. I have inquired of Ruud /Rheem to see if they authorized a substitute pressure switch. Not sure what if anything they will say. The replacement Fasco motor is the only one that Fasco has as a replacement for the original Fasco motor the specs are the same including the RPMs at 3450. This is the second motor I have tried. When the first did not produce the necessary vacuum I exchanged it with the dealer for another of the same model A136. I have made certain that the vent is clear and there is strong exhaust outside.
If I apply external suction to the tube from the switch the furnace will start but it will stop when I run out of breath. Would this happen if the problem was a cracked heat exchanger? I also found that as a quick test if I jumper past the switch the furnace will run. Regardless of the no-start resolution, I will have someone check out the exchanger. Thanks again for all the interest and comment.
Bill

 

[roughneck]

Yes, a cracked heat exchanger can cause a pressure switch issue.

 

[sktn77a]

Could be a stiff switch. Did you try the old one back in?